1. Field of the Invention
The present invention relates to molding tooling and embossing tooling used in molding and embossing micro- and nano-structures, as well as general purpose molding, and in particular to enhanced molding or embossing tooling formed with an attached base with flow through channels for hot and cold fluid, the top of the base being shaped by electro-discharge machining to mate with the uneven bottom surface of the electroformed plate and the method of forming the tooling.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Industries specializing in injection molding, gas-assisted injection molding, slush molding, blow molding, and thermoforming processes strive to mold articles at faster cycle times. Efforts to cut cycle times (and, thereby, manufacturing costs) typically focus on the cooling process, as it is generally the longest part of any cycle. One approach to shortening the cycle time is directed to the mold components (i.e. cavity and core.). Mold components are generally constructed using blocks of metal. The profile or details of the molding surface are typically machined into the metal blocks. Channel patterns, e.g., thermal management channels, are then drilled from various angles such that the channels intersect one another to form thermal management circuits. One drawback of the resulting mold component is that the channels are drilled at straight lines into the metal, and the resulting channel patterns generally cannot conform well to the shape of the intended molded article. This non-conformity causes uneven heat transfer between the mold component and molded article, thus making it difficult to mold products at a faster cycle time and compromising the quality of the molded article (i.e., causing different shrinkage rates due to hot and cold spots in the molded article, resulting in warpage, “sinks”, voids, etc.).
Electroforming has long been utilized to make certain types of mold cavities, when the parts to be therein produced have exceptional requirements of form or surface finish (e.g. optical lenses, microstructures). Electroforms are produced by electrodepositing a metal onto a mandrel, which has the shape which corresponds to (but is opposite in phase from) the mold cavity to be produced (i.e. a convex mandrel is used to make a concave cavity), and subsequently separated from the mandrel. The costs of electroformed tooling are high, however, owing to such factors as the high price of the chemicals and metals needed to maintain the electrolyte from which they are deposited, the electrical energy used, and the relatively slow deposition rate, which necessitates a long process time to achieve significant thickness of the electrodeposit. Nonetheless, for certain applications, electroforming is the only known practical way to produce mold components, and so the practice of electroforming has long been tied to molding.
Electroformed mold components suffer the additional disadvantage of being inherently irregular in shape on their back (i.e. non-molding) surface, except in rare instances wherein the cavity shape is very simple (e.g. optical disc molding). Therefore it is generally necessary for a relatively thick electroform to be produced, in order to account for the loss of thickness that results from post-plating machining of the electroformed component, to bring it to finished dimensions that can be accommodated in an automated molding device. This makes the manufacture of electroformed mold components costly (sometimes prohibitively so).
In injection molding and hot embossing of micro/nano-structures, electroforming is frequently employed as a technique for producing tooling. Often, this is the only practical method for replicating structures of such small feature sizes, with sufficient fidelity. Unfortunately, this presents a problem, as the backsides of electroforms are inherently non-uniform and hence typically require extensive post-plating machining to planarize, or otherwise finish, the back surface of the electroformed tool. This is necessary, in order to facilitate heat exchange between the tool, and the platen against which it is mounted.
Heating and cooling means are typically integrated into this platen or mold base in order to regulate the temperature of the tooling at the tool/plastic interface, where molding/embossing takes place. Quicker, more responsive control of the tool temperature facilitates better replication fidelity, and allows for minimization of process cycle times.
Prior art tooling does not adequately address the problem of minimizing the time involved in the operation while maximizing heating and cooling efficiency of the tooling.
In both micro molding, embossing, and general-purpose molding, Kim, et al (U.S. Pat. No. 6,846,445) taught that molds could be thermally cycled very rapidly, and that conformal cooling was beneficial. However, they passed high frequency current through the mold components to heat them, cleverly taking advantage of the skin effect and the proximity effect, but this approach necessitates some rather cumbersome and costly components, and requires that the mold halves remain within 10 cm of each other during the heating phase. This means that heating cannot take place during part removal, if said removal requires that the mold halves be separated by a distance greater than 10 cm, which is not unusual for deep molds with long cores. They also did not claim nor explain a method indicating how the conformal cooling should be accomplished.
Peterson, et al (U.S. Pat. No. 6,939,123) taught that an electroformed mold component could be made, by laminating an electroformed segment (“stamper”) to a backing block, which is made of machined metal, using an adhesive to bond them together. However, the preparation of such a backing block that would be suitable for a complex shaped electroformed segment, as well as machining the “plurality of projections” described in this patent, require relatively complex and tedious machining operations, and thus this method is also rather cumbersome.
Moore, et al (U.S. Pat. No. 7,004,221) taught a method for manufacturing a mold from two or more joined segments, either or both of which could have some portion of the cooling channel network machined therein, said channel network being conformal to the mold cavity, and joining the two together by employing hot isostatic pressing (HIP), or alternatively using metal tubing to form the channel network, and embedding said tubing in (presumably) powdered metal, which is subsequently densified and joined to another segment or segments by the HIP process. Although this process is perhaps workable for some mold cavities, it does not address the applications (e.g. optics) wherein extremely stringent standards of form and surface finish are required, as it requires the mold cavity to be either cast, or machined. This would not be feasible in many cases, because of the difficulties of generating those forms in a massive mold, unless electroforming were employed to produce those segments. However, electroformed items made of nickel (a very widely applied metal) often contain trace amounts of sulfur, which render them sensitive to the high temperatures typically employed in the HIP process, hence eliminating such electroformed articles as potential mold segments in such a process.
What is needed is embossing and molding tooling formed by a rapid process of attaching a blank to an electroform without having to planarize the back surface of the electroform, the blank having integrated conformal flow-through channels attached as part of the tooling for a quicker, more responsive temperature control with heating and cooling to be facilitated by passing a heat exchange medium (fluid) through the integrated channels in the embossing/molding die.